The present invention relates to a seal structure for an electromagnet lead wire, which includes an insulating resin for sealing the coil of an electromagnet and a seal member through which the electromagnet lead wire extends.
When arranging an electromagnet in a mechanical device to which lubricating oil is supplied, a seal structure configured to prevent the oil from adhering to the lead wires of the electromagnet is necessary. This is because the insulating coating of the lead wires is degraded by the oil.
As a mechanical device incorporating an electromagnet, there is a differential device disclosed in, for example, Japanese Patent Laid-Open No. 6-58347 (literature 1). In this differential device, parts to which oil is supplied and a wet type electromagnetic clutch including an electromagnet and configured to limit an operation are stored the same case. The parts to which oil is supplied are a differential gear mechanism, a main clutch, a ball cam, a bearing, and the like.
The electromagnet disclosed in literature 1 includes an annular yoke, and an exciting coil stored in the annular groove of the yoke. The yoke is attached to the case in a state in which the bottom wall serving as the bottom of the annular groove is in contact with the case of the differential device. The annular groove is filled with an insulating resin used to insulate the coil from outside. The coil is sealed in the annular groove by the insulating resin and fixed to the yoke in this state.
Two lead wires are electrically connected to the exciting coil. These lead wires are extracted from the device through the bottom wall of the yoke and the case. The lead wire outlet of the yoke is provided with a seal member made of rubber in which the lead wires are press-fitted. The seal member prevents oil or rainwater from entering the annular groove through the lead wire outlet. A seal structure having such a seal member can be configured as shown in, for example, FIG. 15.
A seal structure 1 for an electromagnet lead wire shown in FIG. 15 includes a seal member 5 that seals a portion where lead wires 3 of an electromagnet 2 extend through a case 4 of a mechanical device (not shown). The electromagnet 2 includes an annular yoke 6. The yoke 6 is formed into an annular shape with an axis in the left-and-right direction in FIG. 15. The yoke 6 is provided with an annular coil storage groove 7, and is attached to the case 4 in a state in which an annular wall 8 serving as the bottom of the coil storage groove 7 is in contact with a device inner surface 4a of the case 4.
An exciting coil 9 and an annular resin plate 10 are inserted into the coil storage groove 7 together with a coil bobbin 11. The winding start end and the winding terminal end of the exciting coil 9 are connected to the lead wires 3 via solderless terminals (not shown). The lead wires 3 are extracted from the coil bobbin 11 through a lead wire holding portion 12 of the coil bobbin 11 and extend to the outside of the yoke 6 through an insertion hole 13 of the seal member 5. One end of the insertion hole 13 opens to the bottom of the coil storage groove 7, and the other end opens to a concave portion 14 formed at the case-side end of the yoke 6. The concave portion 14 is formed by cutting at the end of the yoke 6.
The coil storage groove 7 and the insertion hole 13 are filled with an insulating resin 15. The exciting coil 9 and the above-described solderless terminals are sealed by the insulating resin 15. A portion of the lead wire 3 extracted from the lead wire holding portion 12 of the coil bobbin 11 extends through the seal member 5 made of an elastic material. The lead wire 3 is fitted in the seal member 5 in a press-fitted state.
The seal member 5 is formed from a columnar portion 17 inserted into a through hole 16 of the case 4, and a plate-shaped portion 18 stored in the concave portion 14 of the yoke 6. The plate-shaped portion 18 is sandwiched and compressed between the case 4 and the bottom surface of the concave portion 14 of the yoke 6. A seal portion 19 having a circular section is provided at the outer edge portion of the plate-shaped portion 18.
According to the thus formed seal structure 1, the lead wire outlet (concave portion 14) of the yoke 6 is sealed by the seal member 5. It is therefore possible to prevent lubricating oil in the case 4 or rainwater outside the case from entering the solderless terminal portions or the exciting coil 9 and also prevent an insulation fault from occurring due to corrosion.
However, if the seal structure 1 as shown in FIG. 15 is used in the field of the wet type electromagnetic clutch of a differential device as described in literature 1, a problem to be described below may arise. The differential device is a device that vibrates. When the vibration is transmitted to the seal structure 1, and the seal structure 1 vibrates for a long time, the insulating resin 15 may peel off from the inner wall surface of the coil storage groove 7 of the yoke 6 or the hole wall surface of the insertion hole 13. If the insulating resin 15 peels off from the yoke 6, a small gap is formed between the insulating resin 15 and the yoke 6, and the oil in the case 4 enters this gap. The oil penetrates to the side of the concave portion 14 through the gap of the peeled portion, moves along the insulating resin 15, and reaches the lead wire 3 from the inside of the concave portion 14. The oil then passes between the insulating resin 15 and the outer surface of the coating of the lead wire 3 and penetrates to the side of the exciting coil 9. For this reason, an insulation fault may occur in the exciting coil 9 due to corrosion.
On the other hand, the oil in the case 4 also enters the concave portion 14 from the joining portion between the yoke 6 and the case 4. If the concave portion 14 is formed by machining, the oil that has entered the concave portion 14 via the entry path can hardly be sealed by the plate-shaped portion 18 of the seal member 5. The bottom surface of the concave portion 14 formed by machining is a cut surface with small unevenness. Even if the plate-shaped portion 18 is brought into tight contact with such a cut surface, it is impossible to completely eliminate gaps. Hence, the oil that has entered the concave portion 14 via the joint surface between the case 4 and the yoke 6 passes between the plate-shaped portion 18 and the bottom surface of the concave portion 14, leaks to the side of the lead wire 3, and penetrates to the side of the exciting coil 9, as described above. Even if the O-ring shaped seal portion 19 with a circular section is provided at the outer edge of the plate-shaped portion 18, the sealing effect cannot be obtained as expected, and improvement is needed from the viewpoint of a moisture resistance and waterproofness.